1. Department of Operative Dentistry and Endodontics, Guanghua School of Stomatology, Sun Yat-sen University and Guangdong Provincial Key Laboratory of Stomatology, Guangzhou 510055, China
2. Biomaterials and Tissue Engineering Division, Department of Endodontics, Periodontics and Prosthodontics, University of Maryland School of Dentistry, Baltimore, MD 21201, USA
3. Department of Endodontics, School of Dentistry, University of North Carolina, Chapel Hill, NC 27599-7450, USA
4. Department of Orthopedic Surgery, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong 510515, China
5. Center for Stem Cell Biology & Regenerative Medicine, University of Maryland School of Medicine, Baltimore, MD 21201, USA
6. Department of Mechanical Engineering, University of Maryland, Baltimore County, Baltimore County, MD 21250, USA